1. Field of The Invention
The present invention relates to scintillating articles and methods of forming same, and more particularly in a preferred embodiment to a scintillating article comprising a barium fluoride film is deposited on an optical waveguide.
2. Description of the Related Art
Scintillating optical fibers are useful as detectors for ionizing particles in high energy physics applications such as radiation track imaging and tracking chambers, calorimetry, synchrotron radiation electron detectors, and pixel detectors for active targets. These fibers can be adapted for use as detector elements in high energy particle accelerators and other high rate experiments.
Current scintillating fibers are drawn from boules of scintillating materials down to sub-millimeter sizes. The scintillation light is captured by total internal reflection and piped out to pixel detectors. The light yields for energy deposited by minimum ionizing particles are 1-2 photons/KeV for cerium oxide glasses and 2-10 photons/KeV for plastic scintillators, the two most common fiber scintillators. By comparison, the crystalline salt NaI yields 40 photons/KeV with a 230 nanoseconds (ns) decay. However, most large crystalline scintillators cannot be drawn into fibers.
The plastic scintillating fibers have excellent scintillation decay temporal properties (1-2 ns decay times) but produce only a few captured optical photons in a few hundred micron thick scintillating optical fiber traversed by a minimum ionizing particle. The fibers therefore require a very high gain pixel detector for good signal-to-noise ratios and also for high bandwidth. Furthermore, these plastic scintillating fibers suffer radiation damage at relatively low doses compared with the potential doses for use in high energy accelerators, and can suffer from other environmental effects such as crazing or water absorption. Although progress has been made in improving the environmental properties of plastics, few long-term tests under realistic radiation exposures have been reported. Furthermore, very long plastic scintillating optical fibers are not useful because of optical self-absorption.
On the other hand, some scintillating glasses, for example, cerium oxides, can be made very radiation-hard. However, scintillating glasses have an even lower low-light output, usually lower than that of plastic scintillators, and also have much longer scintillation decay times (.about.10-50 ns), both of which are undesirable in many high energy applications. Scintillating glasses are also more expensive than plastic.
It is therefore an object of the current invention to provide a scintillating article with (a) very high specific light output, (b) potential radiation-hardness, (c) long-term environmental stability, (d) high dE/dx character and short radiation length compared to plastic, (e) low cost compared to some glasses, (f) high scintillation speed compared to glass fibers, and (g) potentially long attenuation lengths of the emitted light per unit photon output, especially compared with plastic scintillator fibers. It is a further object of the present invention to provide a method for efficient production of these scintillating articles.
Using the scintillating articles of the present invention, a set of imaging radiation detectors can be prepared whose properties can be adjusted for the task at hand. These scintillating optical articles, e.g., scintillating fibers, can be used in medical imaging and diagnostic tools, in industrial non-destructive testing, in industrial x-ray or UV sensors and actuators, in space research, in reactor and nuclear industry monitoring, and in nuclear effects and weapons testing, as well as in high energy physics research.
A grid of properly arranged luminescent fibers according to the present invention can detect the projection of shapes when illuminated by ionizing radiation. Pattern recognition techniques can be easily employed with specific flexible fiber topologies detected by pixel devices. Fibers of such type can also be bundled for extra stopping power, redundancy, or for energy/range discrimination in an x-ray detector.
The scintillating articles of the present invention may be used in image intensifiers or other vacuum photocathode optical imaging sensors. A fine two-dimensional grid of phosphor fibers according to the invention arranged transversely to the photoelectron image, can replace the conventional phosphor screen anode, sampling the image in x-y projections, with the fibers being "read out" conventionally as x-y image information. In high-energy physics, large detectors of this type can be used in RICH detectors.